The "Landing" spot is determined by how far out you have at the least 1 piece of land.
So if you buy out an entire row or column then the landing spot will move. You do not need every piece within that row, just whatever row is the furthest out.
I had this with my town, I was curious how far the right side went and bought to the edge. Then I did the same thing going down. So while I completed each area the landing point didn't continue to update, only when I acquired the furthest piece in that direction.
The same applies to the Squidport expansion, if you aren't buying that furthest section of water, then your landing point will change when you purchase a single plot on that second row/column? of water.
Which brings me to my next point. I'm having trouble figuring if it's 16 x 13 or if it's 13 x 16. Typical sizing is L X W, and I would assume the "length" is going up/down, and "width" is going left to right.
